Bc1 Complex Research Articles

Discovery of Novel Cytochrome bc1 Complex Inhibitor Based on Natural Product Neopeltolide

Background: Natural products (NPs) are important sources for the design of new drugs and agrochemicals. Neopeltolide, a marine NP, has been identified as a potent Qo-site inhibitor of cytochrome bc1 complex. Methods: In this study, a series of neopeltolide derivatives was designed and synthesized by the simplification of its 14-membered macrolactone ring with a diphenyl ether fragment. The enzymatic inhibition bioassays and mycelium growth inhibition experiments against a range of fungi were performed to determine their fungicidal activities. Results: The derivatives have potent activity against the porcine bc1 complex. Compound 8q showed the best activity with an IC50 value of 24.41 nM, which was 8-fold more effective than that of positive control azoxystrobin. Compound 8a exhibited a 100% inhibitory rate against Zymoseptoria tritici and Alternaria solani at a 20 mg/L dose. Conclusion: Computational results indicated that compounds with suitable physicochemical properties, as well as those forming a hydrogen bond with His161, would have good fungicidal activity. These data could be useful for the design of bc1 complex inhibitors in the future.

Quinone binding sites of cyt bc complexes analysed by X-ray crystallography and cryogenic electron microscopy.

Cytochrome (cyt) bc1, bcc and b6f complexes, collectively referred to as cyt bc complexes, are homologous isoprenoid quinol oxidising enzymes present in diverse phylogenetic lineages. Cyt bc1 and bcc complexes are constituents of the electron transport chain (ETC) of cellular respiration, and cyt b6f complex is a component of the photosynthetic ETC. Cyt bc complexes share in general the same Mitchellian Q cycle mechanism, with which they accomplish proton translocation and thus contribute to the generation of proton motive force which drives ATP synthesis. They therefore require a quinol oxidation (Qo) and a quinone reduction (Qi) site. Yet, cyt bc complexes evolved to adapt to specific electrochemical properties of different quinone species and exhibit structural diversity. This review summarises structural information on native quinones and quinone-like inhibitors bound in cyt bc complexes resolved by X-ray crystallography and cryo-EM structures. Although the Qi site architecture of cyt bc1 complex and cyt bcc complex differs considerably, quinone molecules were resolved at the respective Qi sites in very similar distance to haem bH. In contrast, more diverse positions of native quinone molecules were resolved at Qo sites, suggesting multiple quinone binding positions or captured snapshots of trajectories toward the catalytic site. A wide spectrum of inhibitors resolved at Qo or Qi site covers fungicides, antimalarial and antituberculosis medications and drug candidates. The impact of these structures for characterising the Q cycle mechanism, as well as their relevance for the development of medications and agrochemicals are discussed.

S-15176 Difumarate Salt Can Impair Mitochondrial Function through Inhibition of the Respiratory Complex III and Permeabilization of the Inner Mitochondrial Membrane.

Simple SummaryThe metabolic agent S-15176 difumarate salt belongs to a potent class of drugs called partial fatty acid oxidation inhibitors. The possible therapeutic effects of this agent have been widely investigated in models of oxidative damage to different tissues, but the underlying mechanisms are currently unclear and require further research. In the present study, we aimed to investigate in more detail the effect of S-15176 on the mitochondria, power stations inside the cell, and pivotal regulators of many cellular processes. We found that S-15176 affected the key indicators of the function of rat liver and thymocyte mitochondria at the concentrations reached in target tissues. S-15176 disturbed the catalytic function of enzyme complex III of the mitochondrial electron transfer system and induced nonspecific membrane permeability, which was related to the dissipation of the mitochondrial membrane potential and a decline in ATP production. These findings lead us to predict that S-15176 can induce mitochondrial dysfunction in mammal tissues and organs that are most vulnerable to chemical toxicity or exposed to higher concentrations of the drug.S-15176 difumarate salt, a derivative of the anti-ischemic metabolic drug trimetazidine, has been intensively studied for its impact on cellular metabolism in animal models of ischemia-reperfusion injury of the liver, heart, spinal cord, and other organs. Despite evidence of some reduction in oxidative damage to cells, the results of therapy with S-15176 have been mostly disappointing, possibly because of the lack of data on its underlying mechanisms. Here, we aimed to investigate in more detail the role of complexes I-IV of the electron transport chain and membrane permeability transition in mitochondrial toxicity associated with S-15176. Using rat thymocyte and liver mitochondria, we demonstrated that: (1) acute exposure to S-15176 (10 to 50 μM) dose-dependently decreased the mitochondrial membrane potential; (2) S-15176 suppressed the ADP-stimulated (State 3) and uncoupled (State 3UDNP) respiration of mitochondria energized with succinate or malate/glutamate, but not ascorbate/TMPD, and increased the resting respiration (State 4) when using all the substrate combinations; (3) S-15176 directly inhibited the activity of the respiratory complex III; (4) low doses of S-15176 diminished the rate of H2O2 production by mitochondria; (5) at concentrations of above 30 μM, S-15176 reduced calcium retention capacity and contributed to mitochondrial membrane permeabilization. Taken together, these findings suggest that S-15176 at tissue concentrations reached in animals can impair mitochondrial function through suppression of the cytochrome bc1 complex and an increase in the nonspecific membrane permeability.

The plastoglobule-localized protein AtABC1K6 is a Mn2+-dependent kinase necessary for timely transition to reproductive growth

The Absence of bc1 Complex (ABC1) is an ancient, atypical protein kinase family that emerged prior to the archaeal-eubacterial divergence. Loss-of-function mutants in ABC1 genes are linked to respiratory defects in microbes and humans and to compromised photosynthetic performance and stress tolerance in plants. However, demonstration of protein kinase activity remains elusive, hampering their study. Here, we investigate a homolog from Arabidopsis thaliana, AtABC1K6, and demonstrate in vitro autophosphorylation activity, which we replicate with a human ABC1 ortholog. We also show that AtABC1K6 protein kinase activity requires an atypical buffer composition, including Mn2+ as a divalent cation cofactor and a low salt concentration. AtABC1K6 associates with plastoglobule lipid droplets of A. thaliana chloroplasts, along with five paralogs. We show that the protein kinase activity associated with isolated A. thaliana plastoglobules was inhibited at higher salt concentrations, but could accommodate Mg2+ as well as Mn2+, indicating salt sensitivity, but not the requirement for Mn2+, may be a general characteristic of ABC1 proteins. Finally, loss of functional AtABC1K6 impairs the developmental transition from vegetative to reproductive growth. This phenotype was complemented by the wild-type sequence of AtABC1K6, but not by a kinase-dead point mutant in the unique Ala-triad of the ATP-binding pocket, demonstrating the physiological relevance of the protein’s kinase activity. We suggest that ABC1s are bona fide protein kinases with a unique regulatory mechanism. Our results open the door to detailed functional and mechanistic studies of ABC1 proteins and plastoglobules.

A New Approach: Determining cyt b G143A Allele Frequency in Zymoseptoria tritici by Digital Droplet PCR.

Simple SummaryDroplet digital polymerase chain reaction (ddPCR) is an innovative technique for quantifying a target DNA in a diluted target sample, based on the partition of PCR reaction in a large number of sub-reactions (droplets). In recent years there has been an increase in digital PCR (dPCR) utilization in several different fields, and the application of ddPCR in fungicide resistance studies is very recent. Zymoseptoria tritici is the causal agent of Septoria Tritici Blotch (STB), one of the most devasting foliar diseases of wheat grown in temperate climates. STB control relies mostly on fungicide applications and mutations conferring fungicides resistances are concerning phenomena. G143A substitution in fungal cytochrome bc1 confers resistance toward Quinone outside Inhibitor (QoIs) fungicides. In Italy, QoIs are currently sprayed in STB control programs. To the best of our knowledge, we have developed the first ddPCR assay for G143 and A143 alleles detection in samples of gDNA from Z. tritici monocondial cultures. We have also investigated G143 and A143 alleles frequency in Italian Z. tritici populations representative of different fungicide management strategies. The detection of very low G143A substitution percentages in Z. tritici populations is essential for monitoring the emergence of QoIs resistance in field and effectively control STB.Z. tritici first appeared in Italy later than in northern-central European countries. QoIs fungicides currently play a role in STB control, used in combination with Demethylation Inhibitors (DMIs) or Succinate dehydrogenase Inhibitors (SDHIs). In this study, we set up a fast, sensitive, and accurate ddPCR protocol in order to investigate the presence and frequency of G143A substitution, causing a reduction in strobilurins’ efficacy in Z. tritici. The best PCR conditions for the clear separation of positive and negative droplets were identified. The lowest wild-type and resistant alleles frequencies were accurately determined on samples consisting of mixed DNAs from monoconidial cultures of Z. tritici and were expressed as fractional abundance. The protocol was tested by determining the copy number and frequency of alleles on gDNA purified in three Italian Z. tritici field populations representative of different fungicide management strategies. For the first time, the determination of allele concentration and the frequency of a mutation involved in Z. tritici fungicide resistance was carried out by employing digital PCR. This new approach provides a diagnostic tool that is rapid and able to detect very low G143A substitution percentages, which is very useful for fungicide resistance detection at early stages, thus, informing field management strategies for contrasting STB disease.

In silico design, chemical synthesis and biological screening of novel 4-(1H)-pyridone-based antimalarial agents.

Identifying novel lead compounds in drug discovery has been challenging because of the rapid rise of drug resistance to the existing chemotherapeutics and a lack of understanding of complex metabolic pathways in the parasite. Integrating computational and experimental approaches has shown to be of great worth in identifying and developing novel promising pharmacophore hybrids. In this present research, a series of new 4-(1H)-pyridone-derived antimalarial agents were designed based on recent reports and our preliminary findings through in silico studies. Two of the 4-(1H)-Pyridone derivatives showed potential to bind to the Q0 site of the cytochrome bc1 complex and disrupt the mitochondrial electron transport chain. These compounds, along with previously synthesized compounds, exhibited significant inhibitory activities against the malaria parasite. Presently, seven compounds were successfully synthesized, characterized and these novel compounds have shown promise as antimalarial agents.

Structural basis for safe and efficient energy conversion in a respiratory supercomplex

Proton-translocating respiratory complexes assemble into supercomplexes that are proposed to increase the efficiency of energy conversion and limit the production of harmful reactive oxygen species during aerobic cellular respiration. Cytochrome bc complexes and cytochrome aa3 oxidases are major drivers of the proton motive force that fuels ATP generation via respiration, but how wasteful electron- and proton transfer is controlled to enhance safety and efficiency in the context of supercomplexes is not known. Here, we address this question with the 2.8 Å resolution cryo-EM structure of the cytochrome bcc-aa3 (III2-IV2) supercomplex from the actinobacterium Corynebacterium glutamicum. Menaquinone, substrate mimics, lycopene, an unexpected Qc site, dioxygen, proton transfer routes, and conformational states of key protonable residues are resolved. Our results show how safe and efficient energy conversion is achieved in a respiratory supercomplex through controlled electron and proton transfer. The structure may guide the rational design of drugs against actinobacteria that cause diphtheria and tuberculosis.

Anionic Lipids Confine Cytochrome c2 to the Surface of Bioenergetic Membranes without Compromising Its Interaction with Redox Partners.

Cytochrome c2 (cyt. c2) is a major element in electron transfer between redox proteins in bioenergetic membranes. While the interaction between cyt. c2 and anionic lipids abundant in bioenergetic membranes has been reported, their effect on the shuttling activity of cyt. c2 remains elusive. Here, the effect of anionic lipids on the interaction and binding of cyt. c2 to the cytochrome bc1 complex (bc1) is investigated using a combination of molecular dynamics (MD) and Brownian dynamics (BD) simulations. MD is used to generate thermally accessible conformations of cyt. c2 and membrane-embedded bc1, which were subsequently used in multireplica BD simulations of diffusion of cyt. c2 from solution to bc1, in the presence of various lipids. We show that, counterintuitively, anionic lipids facilitate association of cyt. c2 with bc1 by localizing its diffusion to the membrane surface. The observed lipid-mediated bc1 association is further enhanced by the oxidized state of cyt. c2, in line with its physiological function. This lipid-mediated enhancement is salinity-dependent, and anionic lipids can disrupt cyt. c2-bc1 interaction at nonphysiological salt levels. Our data highlight the importance of the redox state of cyt. c2, the lipid composition of the chromatophore membrane, and the salinity of the chromatophore in regulating the efficiency of the electron shuttling process mediated by cyt. c2. The conclusions can be extrapolated to mitochondrial systems and processes, or any bioenergetic membrane, given the structural similarity between cyt. c2 and bc1 and their mitochondrial counterparts.

Ursolic acid as a potential inhibitor of Mycobacterium tuberculosis cytochrome bc1 oxidase-a molecular modelling perspective.

The escalating burden of tuberculosis disease and drastic effects of current medicine has stimulated a search for alternative drugs. A medicinal plant Warburgia salutaris has been reported to possess inhibitory properties against M. tuberculosis. In this study, we apply computational methods to investigate the probability of W. salutaris compounds as potential inhibitors of M. tuberculosis QcrB protein. We performed molecular docking, molecular dynamics simulations, radius of gyration, principal component analysis (PCA), and molecular mechanics-generalized born surface area (MM-GBSA) binding-free energy calculations in explicit solvent to achieve our objective. The results suggested that ursolic acid (UA) and ursolic acid acetate (UAA) could serve as preferred potential inhibitors of mycobacterial QcrB compared to lansoprazole sulphide (LSPZ) and telacebec (Q203)-UA and UAA have a higher binding affinity to QcrB compared to LSPZ and Q203 drugs. UA binding affinity is attributed to hydrogen bond formation with Val120, Arg364 and Arg366, and largely resonated from van der Waals forces resulting from UA interactions with hydrophobic amino acids in its vicinity. UAA binds to the porphyrin ring binding site with higher binding affinity compared to LSPZ. The binding affinity results primarily from van der Waals forces between UAA and hydrophobic residues of QcrB in the porphyrin ring binding site where UAA binds competitively. UA and UAA formed stable complexes with the protein with reduced overall residue mobility, consequently supporting the magnitude of binding affinity of the respective ligands. UAA could potentially compete with the porphyrin ring for the binding site and deprive the mycobacterial cell from oxygen, consequently disturbing mycobacterial oxygen-dependent metabolic processes. Therefore, discovery of a compound that competes with porphyrin ring for the binding site may be useful in QcrB pharmocological studies. UA proved to be a superior compound, although its estimated toxicity profile revealed UA to be hepatotoxic within acceptable parameters. Although preliminary findings of this report still warrant experimental validation, they could serve as a baseline for the development of new anti-tubercular drugs from natural resources that target QcrB.

Virtual Screening, Docking, ADMET and Molecular Dynamics: A Study to Find Novel Inhibitors of Mycobacterium tuberculosis Targeting QcrB

Abstract: A major difficulty in the treatment of mycobacterial infection is its resistance against anti-mycobacterial drugs. Exploration of diverse targets, the search for novel chemical scaffolds and different methods of tuberculosis treatment are all basic measures needed in this perspective. In the same context, mycobacterial oxidative phosphorylation has received a lot of interest. It includes the electron transport system, which encompasses the cytochrome B component of the cytochrome bc1 complex (QcrB) which is a promising therapeutic target. The anti-tubercular drug Q203 (Telacebec), which is currently in phase 2 clinical trial, inhibits cytochrome B. The present study includes virtual screening studies from the ‘Zinc15’ chemical database, taking Q203 as a reference molecule, the creation of protein using homology modeling, molecular docking as well as simulation studies. The constructed protein showed considerable reliability, as results of the Ramachandran plot showed 92.8% amino acid residues in the favoured region, ERRAT score (overall quality factor) of 92.48% with ProSA (Z score) of –5.78. The hit molecules identified by structure-based virtual screening follow the Lipinski rule of five. The docking results indicated binding affinity values ranging from –7.19 to –9.10 kcal/mol. The top three compounds were ZINC64033452, ZINC3816287 and ZINC3830215, each having a higher docking score than the reference ligand (–7.70 kcal/mol). Leu174, Pro306, Ser304, Leu180, Glu314 and Thr313 are among the residues that cover the protein’s active site. The H-bond was observed in docking studies for Q203 and top three molecules from amino acid residues Glu314 and Thr313 and was consistent throughout dynamics studies. In a dynamics run of 20 ns, a stable RMSD was found after 8 ns for hit-molecules and Q203. Based on potential findings, we report that selected candidates are more likely to be used as anti-mycobacterial agents or as starting leads for the development of novel and potent anti-tubercular agents.

Adenine Modification at C7 as a Viable Strategy to Potentiate the Antimalarial Activity of Quinolones.

Although many quinolones have shown promise as potent antimalarials, their clinical development has been slow due to poor performance in vivo. Insights into structural modifications that can improve their therapeutic potential will be very valuable in this vibrant area of research. Our studies involving a library of quinolones which vary in substitution pattern at N1, C3, C6 and C7 positions have shown that the presence of adenine moiety at C7 can bring a noticeable improvement in activity compared to other heterocyclic groups at this location. The most potent compound emerged from this study showed IC50 values of 0.38 μM and 0.75 μM against chloroquine-sensitive and -resistant (W2) strains, respectively. Docking analysis in the Qo site of cytochrome bc1 complex revealed the contribution of a key H-bonding interaction from the adenine unit in target binding. This corroborates with compound-induced loss of mitochondrial functions. These findings not only open avenues for further exploration of antimalarial potential of adenine-modified quinolones, but also suggests broader opportunities during lead-optimization against other antimalarial targets.

FRET measurement of cytochrome bc1 and reaction centre complex proximity in live Rhodobacter sphaeroides cells

In the model purple phototrophic bacterium Rhodobacter (Rba.) sphaeroides, solar energy is converted via coupled electron and proton transfer reactions within the intracytoplasmic membranes (ICMs), infoldings of the cytoplasmic membrane that form spherical ‘chromatophore’ vesicles. These bacterial ‘organelles’ are ideal model systems for studying how the organisation of the photosynthetic complexes therein shape membrane architecture. In Rba. sphaeroides, light-harvesting 2 (LH2) complexes transfer absorbed excitation energy to dimeric reaction centre (RC)-LH1-PufX complexes. The PufX polypeptide creates a channel that allows the lipid soluble electron carrier quinol, produced by RC photochemistry, to diffuse to the cytochrome bc1 complex, where quinols are oxidised to quinones, with the liberated protons used to generate a transmembrane proton gradient and the electrons returned to the RC via cytochrome c2. Proximity between cytochrome bc1 and RC-LH1-PufX minimises quinone/quinol/cytochrome c2 diffusion distances within this protein-crowded membrane, however this distance has not yet been measured. Here, we tag the RC and cytochrome bc1 with yellow or cyan fluorescent proteins (YFP/CFP) and record the lifetimes of YFP/CFP Förster resonance energy transfer (FRET) pairs in whole cells. FRET analysis shows that that these complexes lie on average within 6 nm of each other. Complementary high-resolution atomic force microscopy (AFM) of intact, purified chromatophores verifies the close association of cytochrome bc1 complexes with RC-LH1-PufX dimers. Our results provide a structural basis for the close kinetic coupling between RC-LH1-PufX and cytochrome bc1 observed by spectroscopy, and explain how quinols/quinones and cytochrome c2 shuttle on a millisecond timescale between these complexes, sustaining efficient photosynthetic electron flow.

Targeting the cytochrome bc1 complex for drug development in M. tuberculosis: review.

The terminal oxidases of the oxidative phosphorylation pathway play a significant role in the survival and growth of M. tuberculosis, targeting these components lead to inhibition of M. tuberculosis. Many drug candidates targeting various components of the electron transport chain in M. tuberculosis have recently been discovered. The cytochrome bc1-aa3 supercomplex is one of the most important components of the electron transport chain in M. tuberculosis, and it has emerged as the novel target for several promising candidates. There are two cryo-electron microscopy structures (PDB IDs: 6ADQ and 6HWH) of the cytochrome bc1-aa3 supercomplex that aid in the development of effective and potent inhibitors for M. tuberculosis. In recent years, a number of potential candidates targeting the QcrB subunit of the cytochrome bc1 complex have been developed. In this review, we describe the recently identified inhibitors that target the electron transport chain's terminal oxidase enzyme in M. tuberculosis, specifically the QcrB subunit of the cytochrome bc1 complex.

Structural and functional insights into lysine acetylation of cytochrome c using mimetic point mutants.

Post‐translational modifications frequently modulate protein functions. Lysine acetylation in particular plays a key role in interactions between respiratory cytochrome c and its metabolic partners. To date, in vivo acetylation of lysines at positions 8 and 53 has specifically been identified in mammalian cytochrome c, but little is known about the structural basis of acetylation‐induced functional changes. Here, we independently replaced these two residues in recombinant human cytochrome c with glutamine to mimic lysine acetylation and then characterized the structure and function of the resulting K8Q and K53Q mutants. We found that the physicochemical features were mostly unchanged in the two acetyl‐mimetic mutants, but their thermal stability was significantly altered. NMR chemical shift perturbations of the backbone amide resonances revealed local structural changes, and the thermodynamics and kinetics of electron transfer in mutants immobilized on gold electrodes showed an increase in both protein dynamics and solvent involvement in the redox process. We also observed that the K8Q (but not the K53Q) mutation slightly increased the binding affinity of cytochrome c to its physiological electron donor, cytochrome c 1—which is a component of mitochondrial complex III, or cytochrome bc 1—thus suggesting that Lys8 (but not Lys53) is located in the interaction area. Finally, the K8Q and K53Q mutants exhibited reduced efficiency as electron donors to complex IV, or cytochrome c oxidase.

Synthesis, 3D-QSAR and Molecular Docking Study of Nopol-Based 1,2,4-Triazole-Thioether Compounds as Potential Antifungal Agents.

Cytochrome bc 1 complex is an important component of cellular respiratory chain, and it is also an important target enzyme to inhibit the growth of plant pathogens. Using cytochrome bc 1 complex as the target enzyme, twenty-three novel nopol-based 1,2,4-triazole-thioether compounds were designed and synthesized from natural preponderant resource β-pinene, and their structures were confirmed by FT-IR, NMR, ESI-MS and elemental analysis. The in vitro antifungal activity of the target compounds 5a-5w was preliminarily evaluated against eight plant pathogens at the concentration of 50 µg/ml. The bioassay results showed that the target compounds exhibited the best antifungal activity against Physalospora piricola, in which compounds 5b (R= o-CH3 Ph), 5e (R= o-OCH3 Ph), 5h (R= o-F Ph), 5m (R= o-Br Ph), 5o (R= m,m-OCH3 Ph), and 5r (R= p-OH Ph) had inhibition rates of 91.4, 83.3, 86.7, 83.8, 91.4 and 87.3%, respectively, much better than that of the positive control chlorothalonil. Also, compound 5a (R= Ph) had inhibition rate of 87.9% against Rhizoeotnia solani, and compound 5b (R= o-CH3 Ph) had inhibition rates of 87.6 and 89% against Bipolaris maydis and Colleterichum orbicala, respectively. In order to develop novel and promising antifungal compounds against P. piricola, the analysis of three-dimensional quantitative structure-activity relationship (3D-QSAR) was carried out using the CoMFA method on the basis of their antifungal activity data, and a reasonable and effective 3D-QSAR model (r 2 = 0.944, q 2 = 0.685) has been established. In addition, the theoretical study of molecular docking revealed that the target compounds could bind to and interact with the site of cytochrome bc 1 complex.

Parasitological profiling shows 4(1H)-quinolone derivatives as new lead candidates for malaria

4(1H)-quinolone is an attractive template for antimalarial drug discovery campaigns. Given the current global increase in drug and insecticide resistance, the discovery of new antimalarial drugs is an urgent goal for the fight against malaria. Here, the synthesis and antiplasmodial profiling of a series of 4(1H)-quinolone derivatives are reported. Four compounds showed inhibitory activities in submicromolar range against a panel of sensitive and resistant Plasmodium falciparum strains (IC50s ​= ​0.07–0.48 ​μM) and neither cytotoxic (SI ​> ​210) nor hemolytic activities were observed. Representative compounds of the series showed slow-acting in vitro inhibition, enhanced inhibitory activities over the later erythrocytic forms of the parasite, and submicromolar activity against the ookinete stage (IC50ook ​= ​0.7 ​μM). Evaluation of the mechanism of action indicated that the frontrunner, compound 4 (LSPN182), is a potent (IC50Pfbc1 ​= ​0.5 ​μM) and selective (SI ​> ​120) inhibitor for the cytochrome bc1 complex of P. falciparum. Moreover, the frontrunner exhibited considerable activity against clinical field isolates of both P. falciparum and P. vivax (IC50s of 0.5 and 1.5 ​μM, respectively), a noticeable synergic inhibitory behavior when combined with the antimalarial proguanil (FICindex < 1), and modest oral efficacy at 50 ​mg/kg in a mouse model of P. berghei malaria (45% reduction in parasitemia on day 7 postinfection). Hence, the 4(1H)-quinolone derivatives are attractive chemotypes endowed with relevant in vitro, ex vivo, and in vivo activity.

Cryo-EM structure of the monomeric Rhodobacter sphaeroides RC–LH1 core complex at 2.5 Å

Reaction centre light-harvesting 1 (RC–LH1) complexes are the essential components of bacterial photosynthesis. The membrane-intrinsic LH1 complex absorbs light and the energy migrates to an enclosed RC where a succession of electron and proton transfers conserves the energy as a quinol, which is exported to the cytochrome bc1 complex. In some RC–LH1 variants quinols can diffuse through small pores in a fully circular, 16-subunit LH1 ring, while in others missing LH1 subunits create a gap for quinol export. We used cryogenic electron microscopy to obtain a 2.5 Å resolution structure of one such RC–LH1, a monomeric complex from Rhodobacter sphaeroides. The structure shows that the RC is partly enclosed by a 14-subunit LH1 ring in which each αβ heterodimer binds two bacteriochlorophylls and, unusually for currently reported complexes, two carotenoids rather than one. Although the extra carotenoids confer an advantage in terms of photoprotection and light harvesting, they could impede passage of quinones through small, transient pores in the LH1 ring, necessitating a mechanism to create a dedicated quinone channel. The structure shows that two transmembrane proteins play a part in stabilising an open ring structure; one of these components, the PufX polypeptide, is augmented by a hitherto undescribed protein subunit we designate as protein-Y, which lies against the transmembrane regions of the thirteenth and fourteenth LH1α polypeptides. Protein-Y prevents LH1 subunits 11–14 adjacent to the RC QB site from bending inwards towards the RC and, with PufX preventing complete encirclement of the RC, this pair of polypeptides ensures unhindered quinone diffusion.

Antimalarial Inhibitors Targeting Epigenetics or Mitochondria in Plasmodium falciparum: Recent Survey upon Synthesis and Biological Evaluation of Potential Drugs against Malaria

Despite many efforts, malaria remains among the most problematic infectious diseases worldwide, mainly due to the development of drug resistance by P. falciparum. Over the past decade, new essential pathways have been emerged to fight against malaria. Among them, epigenetic processes and mitochondrial metabolism appear to be important targets. This review will focus on recent evolutions concerning worldwide efforts to conceive, synthesize and evaluate new drug candidates interfering selectively and efficiently with these two targets and pathways. The focus will be on compounds/scaffolds that possess biological/pharmacophoric properties on DNA methyltransferases and HDAC’s for epigenetics, and on cytochrome bc1 and dihydroorotate dehydrogenase for mitochondrion.

In-silico design and ADMET predictions of some new imidazo[1,2-a]pyridine-3-carboxamides (IPAs) as anti-tubercular agents

Tuberculosis (TB) is one of the leading infectious diseases worldwide even with the ravaging COVID-19 pandemic in recent times. This mandated further search and exploration of more possible anti-TB drug candidates against M. tuberculosis strains. As an extension of our previous work on the homology modeled cytochrome b subunit of the bc1 complex (QcrB) of Mycobacterium tuberculosis, an in-silico design was carried out in order to further explore more newly potential anti-TB compounds. Ligand 26 was selected as the lead template (scaffold A) based on our previous docking results and its less bulky structure. Successively, eight (8) new ligands (A1–A8) were designed with better binding affinities in comparison to the scaffold template (−6.8 kcal/mol) and isoniazid standard drug (−6.00 kcal/mol) respectively. In addition, three (3) designed ligands namely, A6, A2, and A7 with higher binding affinities were validated via ADME and toxicity prediction analysis, and the results showed zero violations of Lipinski rules with similar bioavailability, and high rate in gastrointestinal absorption, while toxicity parameters such as carcinogenicity and cytotoxicity were all predicted as non-toxic (inactiveness). The designed IPA compounds in the present study could serve as a promising gateway that could help the medicinal and synthetic chemist in the exploration of a new set of derivatives as anti-TB agents. Therefore, this research strongly recommends further experimental consideration of the newly designed IPA compounds through synthesis, in-vitro and in-vivo studies to validate the theoretical findings.

Cryo-EM structure of the Rhodospirillum rubrum RC-LH1 complex at 2.5 Å.

The reaction centre light-harvesting 1 (RC–LH1) complex is the core functional component of bacterial photosynthesis. We determined the cryo-electron microscopy (cryo-EM) structure of the RC–LH1 complex from Rhodospirillum rubrum at 2.5 Å resolution, which reveals a unique monomeric bacteriochlorophyll with a phospholipid ligand in the gap between the RC and LH1 complexes. The LH1 complex comprises a circular array of 16 αβ-polypeptide subunits that completely surrounds the RC, with a preferential binding site for a quinone, designated QP, on the inner face of the encircling LH1 complex. Quinols, initially generated at the RC QB site, are proposed to transiently occupy the QP site prior to traversing the LH1 barrier and diffusing to the cytochrome bc1 complex. Thus, the QP site, which is analogous to other such sites in recent cryo-EM structures of RC–LH1 complexes, likely reflects a general mechanism for exporting quinols from the RC–LH1 complex.